Aim: Previous animal studies suggested that vagal tone contributes to tonic dilatation of coronary arteries. We hypothesized that low parasympathetic activity might be among the causes of coronary instability in the setting of acute coronary syndrome without ST-segment elevation.
Methods and results: We studied 172 consecutive patients. Vagal and sympathetic activities were assessed by time domain measures of heart rate variability. PNN50 <3% was used as a marker of low parasympathetic activity. At 6-month follow-up 32 patients developed coronary events. Coronary events were lower during hospitalization (n=9) than during follow-up (n=23). Extremely low values of parasympathetic activity (pNN50 <3%) were strongly related to subsequent events (P<0.001). PNN50 <3% was found in 56% of patients having adverse events versus 5% of patients who had good outcome. Among patients who had pNN50 <3%, 18 patients (72%) had subsequent coronary events vs seven patients (28%) who had a good outcome.
Conclusions: These data show that in acute coronary syndrome without ST-segment elevation, a significant number of patients developing subsequent coronary events have a loss of vagal tone. Simple electrocardiographic variables, as pNN50 <3%, may be of great clinical value in identifying patients at high risk of subsequent coronary events even after apparent clinical stabilization.